Method of and apparatus for the



May 16, 1944. H. BLOOD 2,348,831

MBTLLIOD OF AND APPARATUS FOR THE GENERATIVE .FORMATION OF SURFACES 0FOVATE SECTIONS Filed Feb. 19. 1941 ,s Sheets-Sheet 1 giwwm HaroldL.Blood.

5 Sheets-Sheet 2 ERATIVE VATE SECTIONS H. L. BLOOD APPARATUS FOR THE GENMETHOD 0F AND FORMATION OF SURFACES OF 0 Filed Feb. 19, 1941 May 16,1944.

y 1944. H. BLOOD METHOD OF AND APPARATUS FOR THE GENERATIVE FORMATION OFSURFACES OF OVATE SECTIONS Filed Feb. 19, 1941 5 Sheets-Sheet 5 PatentedMay 16, 1944 UNITED- STATES PATENT OFFICE METHOD OF AND "APPARATUS FORTHE GENERATIVEv FORMATION OF SURFACES OF OVATE SECTION Harold L. Blood,Worcester, Mass, assignor to The Heald Machine Company,

Worcester,

10 Claims.

The present invention relates: to the direct. generation (i. e., withoutresort to copying from a master or pattern). by machining, boring,grinding or the. like, of. exterior or interior surfaces that are.slightly ovate. or noncircular in cross section. Examples of. suchsurfaces are the. cylinder bores required for certain fluidmotors,pumps, compressors etc.. of the rotary type. viz: those. wherein. theusual. eccentrically-mounted rotor or drum has a diametrally slidablevane or piston. of substantially one-piece or constantlengthconstruction. Ihe operation of such a vane requires. a cylinder bore ofapproximately the sectional contour defined by a symmetrical limaconcurve which. is equi-metrical in all directions through. a pointcorresponding to the center of the eccentric drum or rotor, namely. thecurve which is traced. by the ends of a series of equallength chords allpassing through the same interior point, and whose perpendicularbisectors pass through. the. center of the inscribed circle.

For the formation of a bore surface of such curvature, it has heretoforebeen proposed to eccentrically rotate the cylinder in a lathe with itsdrum or rotor axis in alignment with. the lathe axis,v thus. to'obtain,by the horizontal. component of the cylinders eccentric motion, thereciprocation of a cutting, tool which engages the cylinder bore in thehorizontal plane. of. said. lathe axis. Theoretically, this previouslyproposed method will cause the, desired non-circular curvature to bedescribed. by the tool. point. on the eccentrically-rotatingworksurface; but-in the practice of this method, great. difficulties areencountered in the cutting action. of. the tool.. One. of thesedifiiculties stems. from the off-center rotation of the work, whichcompels. the point of cutting to constantly shift between positions farabove and far below the cylinder bore axis; these changes. of cuttinglevel,. relative to: the concave. surface ofthe work, involve suchextreme variations in the rake and clearance angles of the tool thatnouniformity of. cutting action is obtainable. Another difficulty of thispreviously proposed method is the relatively great amplitude: ofreciprocatory tool travel, over a. distance which is double theeccentricity of thebore and drum axes, and thus, far in excess. of? theactual departure. of the desired curve from its inscribed.- circlethisinvolving periodically such rapid feeding movements of the tool into thesurface of the rotating work that excessive. cuttingpressures and rapidtool Wear are inevitable.

It has. also been proposed to. hold thework. from rotation, and. to.machine its bore to the. desired 65,

non-circular cross-section by a rotary and slidably-mounted cutting toolwhich, in revolving. about an axis corresponding to that of thecylinders eccentric rotor or drum, is constrained to slide in and out,togive the tool pointa noncircular path of the desired curvature; Buthereagain there are wide variations in the rake and clearance angles ofthe tool; moreover the tools cutting poi-nt. is compelled. to pass veryrapidly over certain: portionsof the work surface and very' slowly overother portions: of the work. surface, so that no uniformity of cuttingactiorr is obtainable. 1

My invention overcomes all. these difficulties;

- by machining or cutting the work bore to the;

desired. ovatesection: in a. manner which permits. the relative:rotation between tool and workpiece to take: place on. the true. axis ofthe workpiece. bore, and which. allows the tool to have an abso--lutely' uniform cutting speed with no appreciable variations in its?rake and; clearance angles; moreover, the. reciprocation. of the tool isof. very small: amplitude, at notime exceeding. the maximum. departureof the desired section from its inscribed vcirclez. Other and. furtherobjects and. advantages of my invention will more fully appear from thefollowing detailed description, taken: in.

connection with the; accompanying illustrative drawings, in whichFig. 1. is. a. sectionalview showing: the essential elements of. a vanetype. pump or compressor, when a constant-length: vane is used.

Fig. la is a view similar to Fig; 1, showing. a. slightly different vaneconstruction.

Fig. 2 is a diagram illustrating the nature of the sectional contourrequired for a cylinder bore adapted to accommodate a van-e of thetypeshow-n by Fig.1".

Fig. 2a is a similar diagram for a cylinder bore adapted to accommodatea vane of the type shown by Fig. 1a.

Fig. 3 is a schematic view, illustrating the principles of my generativemethod, as. applied to the machining. of. the; contour represented. byFig.. 2.

Fig, 4 is a. view in front elevation of a. boring machine: organizationarranged in. accordance with: my invention to: generate the desired.surface. contour.

Fig. 5 is a top plan view of themachine of Fig. 4.

Fig. 6 is a larger scale: fragmentary end elevation of said machine, asviewed from the right Fig. 4.

Fig. 7 is a sectional View, on the line 1-1 of Fig. 6.

Fig. 8 is a large scale front elevation of the tool head of saidmachine.

Fig. 9 is an end elevation of said head as viewed from the left, Fig. 8.

Like reference characters refer to like parts in the different figures.

I have shown very simply in Fig. 1, the elements of a vane type pump orompressor having the conventional eccentric rotor or drum A, but thelatters vane instead of being the well-known variable-length device foroperation in a cylinder chamber of circular cross section, is aconstantlength vane B slidable diametrically in said rotor. Such aconstant-length vane B requires for its operation a cylinder chamber orbore whose interior boundary surface is slightly non-circular in crosssection, the same being typified, for example, by the curve D (Fig. 2)of the'limacon order,

such as would be traced or generated by the terminal points a and b of asuccession of equallength chords L, L,- etc. (corresponding to thelength of the vane), all passing through the same point P (the center ofthe eccentric rotor) which is at a fixed distance R. from the center Cof the inscribed circle E; as shown in Fig. 2, each chords perpendicularbisector Z passes through said center C.

My improved method-of generating the substantial equivalent of thiscross-sectional contour D is depicted diagrammatically by Fig. 3,wherein the point P represents a crank which follows a circular path ofradius R about a center C; this crank is shown in engagement with asuitable slot s of a lever f, pivoted to rock, in response to saidcranks rotation, about a fulcrum point b; the lever 7 provides at itsother end a plane surface-g, which is at a distance in from fulcrumpoint D. Cooperating with surface g is an arcuate surface J, provided bya slidably mounted bar 112. carrying a cutting tool whose point isindicated at t-the arrangement providing a spring 12 or the like bywhich to maintain contact of surface J with surface 9. The tool it isshown in operative relation to the bore W of a piece of work (such as apump cylinder of the type shown by Fig. 1) which isrevolved about theaxis of its bore at the same angular speed a that imparted to the crankP.

- The arcuate surface J, Fig. 3, is struck from a center oraxis J onsucha radius (70) that the sum of the distances hand k is equal to one halfthe length and are identical, since Therefore in the angular position ofparts shown by Fig. 3, the distance X between points I) and of the crankP and work W, will be caused,

by the movements of bar m in response to rolling of surface 9 on surfaceJ, to vary its distance from the work center 0 in nearly the sameproportion as the terminal point b of chord L varies its distance fromcenter C in tracing the curve D,. Fig. 2.

The cross-sectional contour generated in the bore of rotating work W bythe tool t may vary slightly from the curve D, because of the fact thatthe fulcrum point '0' is fixed rather than movable. But the error ordeviation is wholly negligible in practice. Actually the angle Cb'P' hasthe same value as shown in Fig. 3 at four different points in eachrevolution of the crank, and at each of these points, as demonstratedabove, the distance from o to t exactly equals the distance from C to b.This'equality also prevails each time the angle CbP' passes throughzer0making six points wherethe correspondence isexact. At intermediatepoints the differ ences between the angle Cb'P' and CbP are so slightthat the deviation from curve D of the contour produced by tool t isnegligible, being well within practical working tolerances.

The adaptation of the principles above set forth to a machine forgenerating a surface of revolution having the desired non-circularcrosssection, is shown by Figs. 4 to 9 inclusive. As shown in Figs. 4and 5, said machine Provides a suitable base I, having longitudinalways, not shown, for the support of a reciprocatory'table or slide 2. Abridge 3 spanning said ways and said table, supports a head or mounting4 wherein is suitably journalled a work-rotating spindle 5; the lattercarries at one end a suitable holder 6 in which the work W is chucked,and at the other end a pulley 1 which may be connected as shown by abelt 8 to a drive pulley 9 on the shaft I0 of a motor or other primemover, employed for the rotation of the work W.

The bridge 3 also carries a suitable bracket ll, having spaced bearingportions l2 and I3 wherein are rotatably mounted the sleeves I4 and I5.Slidably received in' these rotatable sleeves is the polygonal endportion IE or an elongated shaft l6, said end portion l6 being slidableendwise through a gear I! mounted thereon and meshing with a gear 18 ofthe same size on spindle 5 -any suitable means, such as a fixed housingl9 secured to head 4, being employed to hold the gear II againstshifting endwise with shaft'wlfi, thus to insure the latter's rotationat the same speed as spindle 5. a This provision for endwise movement ofshaft l6 grows out ofthe fact that its other end is supported andcarriedby the reciprocatory table 2; the latter having mounted thereonasuitable bracket 20, providing a housing 2| in axial 'alin'ement withsaid'shaft and containing bearings 22 (Fig. '7) for the reduced end 23ofsaid shaft. Beyond said bearings the shaft has an eccentric pin or crankextension 24, the latter entering and being turnable in a block 25 whichis held on said crank by a nut 25'.

The bracket'ZD provides suitable housings 26 and 21 for'bearings 28 and29 in which is Journalled, below shaft l6, 2. rock shaft 30, the latterhaving an intermediate cut-away portion 3| wherein is secured a hardenedpad 32 whose fiat working surface, facing downwardly, is on a diameterof said shaft; that is, the shaft axis is contained by said surface, andthe latter, at the middle of said shafts rocking movement occupies thehorizontal plane of. said axis. Secured to rock shaft 30, as by apin 33is the hub 34 of a yoke member 35, the latter extending upwardly aroundthe crank 24, and providing interior parallelguide surfaces 36 and 31(the latter on a cap 38) in opposed relation. The block 25 has. endsurfaces (shown by broken lines in Fig. 6) which are in sliding contactwith these guide surfaces 36 and 3|-whereby at each revolution of shaft|6,.said block 25, under the infiuence of crank 24, gives yoke 35 andwith it the attached shaft 30 a back and forth rocking movement, similarto that of lever f in the diagram of Fig. 3. Also by analogy with Fig..3, the center-to-center distance between shafts I6 and 30 and theradius of crank 24 are so chosen and proportioned as to be in the ratioto b R (Fig. 2) of the curve to be generated.

The bracket 20 of table 2 also supports a trunnion shaft39, parallel tothe rock shaft 30 and offset therefrom a definite distance ashereinafter described. Mounted for rocking movement about the axis 43 ofshaft 33 is a bell-crank member 4|, having a generally horizontalportion 42 whose free end underlies the rock shaft 30, and having agenerally upright portion 43, for the support of a tool, as hereinafterdescribed, adapted to operate in the bore of work W during the lattersrotation by'the work spindle 5. The portion or arm 42 has securedthereto, as by suitable bolts 41, an upwardly extending post 44,carrying at the 'top a hardened-wear pad 46 whose convex upper surface,struck from an axis 45, is contacted by the flat under surface of wearpad' 32' on rock shaft 30. Such contact is maintained by a spring 48here shown as seated on bracket 20 and thrusting upwardly against thearm 42. The minimum distance between the axis 45 and the axis of shaft30 is made equal to one-half the chord length of the curve (Fig. 2)required to be generated. The axis 40 is equidistant from the axis ofwork rotation and from the axis of rock shaft 30; that is to say, asshown in Fig. 6, an are 49 struck from 40 as a center will pass throughthe axis of shaft 33 (about which rocks the yoke 35) and also throughthe axis (shown by point 50, Fig. 6) of the workspindle 5. As previouslystated, the upright arm 43 of rockable member 4| supports the toolwhich, by movement of table 2 to the left, Fig. 1, is traversed from oneend to the other of the bore of the rotating work W, to generate thedesired surface of non-circular cross-section along the full length ordepth of said bore.

The point of said tool is indicated in Fig. 6 by numeral the distance ofsaid tool point 5| from work bore axis 50 determines and establishes thespacing (see X Fig. 3) of axis 45 from rocker axis 35, and as thisspacing changes slightly, in response to rolling of surface 32 onsurface 46, so will the tool point 5| vary its distance from work axis50, since the triangles 30, 40, 45 and 50,40, 5| remain equal, for anygiven setting or adjustment of the machine, and always swing together.

It will be understood that the tool point 5|, in addition to itsabove-described in and out movements relative to work center 50, iscaused by table 2 to traverse the bor of the work, thus to impart thedesired cross-sectional contour all the way along said bore. The backand forth travel of the table 2 may, of course, be effected by anysuitable means, such as the usual fluid-pressure actuated devices, notshown, whose controls are indicated at 2', Fig. 4.

As shown in Figs. 8 and 9, the tool-supporting arm 43 may be equippedwith two tools 52 and 53, the former for a roughing operation and thelatter for a subsequent finishing operation, these two operations beingperformed with a single chucking of the work W. The tools 52 and 53 arearranged 180 apart in a head 54, the latter beingmovable between twodifferent positions-to dispose selectively either the tool 52 or thetool 53 in theworking position represented at 5|,-Fig. 6. To this end,the tool carrying head 54 is mounted on a shaft 55, the latter extendingthrough andbeing supported by the arm 43 and the latters attachedoverhanging bracket 56. A collar 5'! secured to shaft 55 keeps theopposing faces of head 54iand bracket 56 in close contact. The head54Lprovides index holes 58 and 59 which are'180" apart, and which, byturning of shaft 55 are selectively registrable with a pin Gil. slidablymounted in the bracket 56, and pressed toward said-head by a spring 3|.Entrance of pin 69 into hole 58, as shown in Fig. 8, looks the head 54in the angular position which makes the roughing tool-52 operative; whenit is desired to operate with finishing tool 53, the pin 5! is retractedby means of its handle 52, this allowing the shaft 55 to be turned, byits handle 63, through I", to aline the other hole 59 with pin 55, forlocking the head in the angular position where said finishing tool 53,instead of the roughing tool 52, is operatively associated with thework, in the position 5| of Fig. 6.

Fig. in shows the same pump arrangement as Fig. 1, except that theconstant-length vane B has convex, rather than chisel-point, ends. Themethod and means for generating the interior boundary surface D of thepump chamber is the same as above described for the surface D of Fig. 1,except as affected by the need to take account of the radius ofcurvature of the convex ends of the vane.- This may be done by utilizingfor the cutting operation a grinding wheel or milling cutter having aradius of curvature substantially equal to that of the ends of the vane.Or, a close approximation of the desired contour, by a cutting tool ofthe type shown at t in Fig. 3, can be obtained, as shown in Fig. 2a, ifthe tool point be set out a distance equal to the vane-end radius, fromthe curve or contour D which is traced, as heretofore described, by aconstant-length chord L (the distance between the vane-end centers). Thedifference in Fig. 2a between the contours'D and D is due tothe angle ofcontact a between the end of the vane and the'surface D.

- I claim:

1. Apparatus of the class described, for cutting a workpiece bore to anon-circular section approximating the curve traced by the ends ofequal-length chords passing in different direc-

